hibernate 简单笔记（二）

记录一个hibernate一对多的例子。

前提：

1. 当前有表t_book，如hibernate简单笔记（一）中的例子；

2. 建立新表t_owner:

CREATE TABLE t_owner(
    id INT AUTO_INCREMENT PRIMARY KEY,
    book_id INT,
    myname VARCHAR(30) NOT NULL,
    FOREIGN KEY(book_id) REFERENCES t_book(id));

一.生成对象关系映射文件TOwner.hbm.xml，并在hibernate.cfg.xml中添加mapping。下述例子中由Myeclipse自动生成：

<hibernate-mapping>
    <class name="com.TOwner" table="t_owner" catalog="db_fredric">
        <id name="id" type="integer">
            <column name="id" />
            <generator class="assigned" />
        </id>
        <many-to-one name="TBook" class="com.TBook" fetch="select">
            <column name="book_id" />
        </many-to-one>
        <property name="myname" type="string">
            <column name="myname" length="30" not-null="true" />
        </property>
    </class>
</hibernate-mapping>

二.创建持久类，注意不同的地方是属于外键的那个属性被替换为一个类：

public class TOwner {
    private Integer id;
    private TBook TBook;//映射TBook类
    private String myname;
    public Integer getId() {
        return id;
    }

    //略

三.操作

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Configuration con = new Configuration();
        con.configure();
        
        SessionFactory sessionfactory = con.buildSessionFactory();
        Session session = null;
        Transaction tran = null;
        try{
            session = sessionfactory.openSession();
            tran= session.beginTransaction();
                    
            TOwner owner = (TOwner) session.get(TOwner.class, new Integer(1));
            System.out.println(owner.getTBook().getBook());
            System.out.println(owner.getTBook().getName());
            System.out.println(owner.getMyname());
            
            tran.commit();
        }catch(RuntimeException e){
            if(null != tran){tran.rollback();}
        }finally{
            session.close();
        }
    }
}

如上例通过t_book中的外码，相应的book记录也被取出。